For a traditional lithium-ion electrode, a slurry of materials is spread on an aluminum or copper substrate and then dries in a series of enormous ovens. This requires huge amounts of both time and energy. But Tesla aims to press dry powdered electrode materials using giant rollers. The process is based upon one created by Maxwell Technologies; a company recently purchased by Tesla. The big advantage is an up to 7 times increase in output per battery production line. “Tesla is aiming to be the best at manufacturing of any car company on Earth,” said Musk. Tesla reports the dry cathode reduces the line footprint to the extent that a 1 TWh sized plant could fit in the same space as a current 150 GWh plant.
Others have been working with various amounts of silicon mixed with graphite for lithium-ion battery anodes. Silicon can hold more lithium ions than carbon graphite and is much cheaper, but has some problems. “The challenge with silicon is that it expands four times when charged with lithium,” according to Baglino. This can cause cracking and reduce the capacity of the anode. Most who have worked with silicon start with silicon dioxide—sand. Tesla instead has started with metallurgical raw silicon and then stabilizes the surface with, “…an elastic ion-conducting polymer coating that’s applied through a very scalable approach,” said Baglino. “We can increase the range of our vehicles an additional 20%,” said Baglino, while also producing a cheaper anode, reportedly about 5% less in dollars per kWh. A lack of additional details makes it difficult to determine the viability of the Tesla silicon anode.
The chemistry of the cathode has a significant effect on the performance and price of a lithium-ion battery. High amounts of nickel in the cathode provides high energy densities and power outputs. Nickel mining is typically a byproduct of copper mining and is rarely optimized. This means that it requires large amounts of sulfuric acid and water—a recipe for environmental disaster. Instead, Tesla proposes to eliminate the nickel sulfate phase in the mining and to use nickel ore in the development of its high nickel content cathodes.
Nickel cathodes, while producing maximum performance can be unstable, which is why cobalt is added to the mixture. Cobalt stabilizes the cathode structure but is both expensive and is sourced largely from a politically unstable country with questionable and sometimes unethical labor practices. Right now, Tesla uses cathodes made from nickel, cobalt, and aluminum (NCA) for its EVs and nickel, cobalt, and manganese (NCM) for its stationary power storage batteries. It also has some much cheaper lithium, iron, and phosphorous (LFP) cathodes supplied for its Chinese versions of the Model 3. Nickel cathodes are about 50-60% better than LFP, but for medium-range EVs (less than 300 miles), LFP can be used.
Tesla says that eliminating cobalt from a high-nickel cathode improves costs by 15% on a per kilowatt-hour basis. It's not exactly clear how Tesla plans to make an all-nickel cathode work, but the company said that when it builds its own cathode plant in the US, it will be able to reduce the cost of processing by 76%, while also reducing the amount of water needed for the raw materials. By building its own cathodes, Musk also claims that recycling the batteries after use will be easier and more economically viable.
Like nickel, mining lithium uses vast amounts of water that must be treated before it can be returned to the environment. “Lithium is like oil—there’s lots of lithium everywhere,” said Musk. Much of lithium mining is done in traditional ways and Musk hopes to change that for lithium supplied to his battery plants. The company has purchased a 10,000-acre site in Nevada where it will separate lithium from clay deposits through a new, much simpler process and ship the lithium directly to the company’s Nevada Gigafactory. Musk claims that there is enough lithium just in Nevada to supply all of the US EV needs.
Structural Battery Pack
Typically, in an EV, battery cells are grouped into modules that are then combined into packs. Packs go into protective casings, often under the floor of the car. The result is heavy, which degrades performance and range.
At the Battery Day presentation, Musk and Baglino described a new Tesla idea. The company already has the world’s largest high-strength aluminum casting machine at its Fremont plant. The idea is to make the front and rear sections of the car as single cast aluminum pieces and then tie them together with the pack, located between them. The pack will act as a honeycomb structure, with shear plate aluminum skins on the top and bottom surfaces and the 4680 cells located between the plates to create a stiff structure. There will be no modules or separate case and the pack itself is a stressed structural element that ties together the front and rear of the car. Tesla expects this configuration will give a 14% range increase while requiring 370 fewer parts to build.